Similiar to "remove from flow", there should be a flow step that says "pause from flow" which temporarily suspends a lead from the campaign, then waits for a particular action to trigger "resume flow" from the point at which the "pause fom flow" occurred.
This would be useful for many things, but one example might be when a lead is prematurely removed from a nurture campaign, and you want to put that lead back in the nurture campaign but not start them from the beginning.
I can think of a couple work arounds for this, but they would be ridiculously time consuming and complex. If there is another way to do this I don't know it.